In WCDMA system, the uplink capacity is loosely managed in such a way that a mobile station can transmit up to a maximum rate that is controlled by a Radio Network Controller (RNC). The RNC based statistical multiplexing scheme would result in a high noise rise variation that leads to a loss of uplink capacity due to a large required noise rise headroom.
As a sister technology of HSDPA, a closed-loop-based uplink capacity scheduling between mobile station and base station is recently proposed in 3GPP. A reference is Non-Patent Publication 1 (3GPP TR25.896 v1.0.0 “Fesibility Sudy for Enhanced Uplink UTRA FDD” (2003-9)). In EDCH, a base station controls the maximum capacity of mobile station instead of RNC in such a way that the noise rise of cell is controlled in order to achieve smaller variance. The base station can react faster than RNC to the fast changing nature of wireless channel. Therefore the capacity scheduling at base station has a natural advantage over the RNC based WCDMA capacity scheduling. There are two kinds of scheduling schemes currently under investigation namely, ‘Rate Scheduling’ and ‘Rate and Time Scheduling’.
In WCDMA system, the priority handling in uplink packet data transmission is such that a higher priority data packet is transmitted prior to lower priority data packet. Therefore a data packet with highest priority will be served up to maximum available transmission rate of mobile station, and if there is remaining rate, the next highest priority data packet can be transmitted. In addition to priority handling, a QoS handling was introduced in HSDPA, namely Guaranteed Bitrate (GBR). This is a kind of QoS-aware radio capacity scheduling in downlink packet transmission in such a way that the packet scheduler is aware of QoS requirement of data packet in addition to its priority to provide sufficient radio capacity to meet the required QoS of data packet.
In WCDMA system, a mobile station can assign uplink capacity for multiple data flows using a “set” of Combination of Capacities (CC). Each CC in the set indicates how a total capacity is divided into multiple flows while each CC may have different amount of total capacity TC in FIG. 1. Therefore, RNC can limit the total uplink transmission capacity by restricting mobile station to use only an allowed “sub-set” of CC. The required signaling is, then, an indication of the sub-set of CC from RNC to mobile station.
Similarly, in EDCH system, the base station can limit the total uplink transmission capacity by restricting mobile station to use only an allowed “sub-set” of CC. An efficient signaling technique, namely Pointer Handling, is proposed to reduce the overhead associated with the required signaling of the sub-set of CC between the base station and mobile station. This scheme requires the set of CC to be ordered with respect to the total amount of capacity. For example, the CC in FIG. 1 is ordered with respect to total capacity into FIG. 2. Then, the base station uses a differential signaling (i.e. +1 or −1) in signaling of the allowed sub-set of CC, e.g. at every beginning of capacity scheduling interval, a differential signaling is sent to all mobile stations in the cell. In addition, the mobile station can request to modify the allowed sub-set of CC, if it's allowed subset and cannot meet the priority and QoS of data flows. Then, a conventional differential signaling can be also used as request to modification of allowed sub-set of CC so that mobile station sends +1 or −1 if it requires higher or lower capacity. The differential signaling limits the overhead of signaling the allowed set of CC in order to conserve the uplink and downlink capacity for data transmission.
Despite of its spectral efficiency, the conventional differential signaling has a latency problem when it is applied to multiple data flows. In the example shown in FIG. 2, if the mobile station wants to reduce or increase the capacity allocated for a specific flow, then more than one differential signaling message is needed to be signaled. For example, if the current Pointer indicates CC3 and mobile station wants to increase the flow capacity of Flow 2 to 64 kbps, then two consecutive +1 signaling are needed and therefore the latency of capacity scheduling is increased. If the total size of the set of CC increases by introducing finer granularity of each flow, the latency will be also further increased so therefore the effectiveness of capacity scheduling is reduced.
The conventional differential signalling has a coupling problem when it is applied to multiple data flows. In the example shown in FIG. 2, if the current Pointer indicates CC3 and the mobile station wants to increase capacity of Flow 1 to 128 kbps while maintaining capacity of Flow 3 at 8 kbps, two consecutive +1 signaling are needed. After 1st +1 signaling, Pointer indicates CC2 in which Flow 3 cannot transmit a data at all. This problem will be even more complicated if finer granularity for multiple flows is to be supported.
Handling of multiple priority and QoS of multiple flows is also a problem of differential signalling. If a flow is high priority and other flows are low priority flows, the latency of capacity change of high priority flow is delayed by granularity in low priority flows. For example in FIG. 2, if Flow 1 is high priority flow, in order to change a capacity, it requires two consecutive differential signaling. The problem becomes more complicated if the granularity of low priority is increased or total number of multiplexed flows is increased. There should be a mean to enable faster adaptation based on flow priority and associated QoS.
With reference to FIG. 3, consideration is given to a case in which a mobile station 1 and a mobile station 2 each have a plurality of flows having different priorities. In the mobile station 1, a flow 1a with high priority requests increase of the capacity, whereas a flow 1b with low priority requests reduction of the capacity. In the mobile station 2, a flow 2a with high priority requests reduction of the capacity, whereas a flow 2b with low priority requests increase of the capacity. According to the conventional differential signaling, each mobile station synthesizes the capacity requests of the plurality of flows into a single capacity request and reports this capacity request to the base station. Accordingly, in the example shown in FIG. 3, both the mobile station 1 and the mobile station 2 transmit a single capacity increase request. However, the base station cannot identify which flow of the mobile stations requests the increase of capacity. Therefore, it is impossible to preferentially allocate the capacity to the high-priority flow when the remaining capacity is not enough and the base station is only able to respond to the capacity increase request from one of the mobile stations. This induces a problem that the QoS achievement rate of the system as a whole is deteriorated.